The present invention relates to electro-optical displays of the type using electrochromic material which undergoes reversible color changes upon the application of an electric field.
More particularly, the present invention relates to a coloration uniforming circuit adapted for the electrochromic display to provide uniform coloration regardless of the surrounding temperature adjacent to the display.
There are two types of electrochromic displays referred to as ECDs hereinbelow. (See, for example, L. A. Goodman, "Passive Liquid Displays" RCA Report 613258). In one kind, the color variation is produced by the changes in the opacity of an inorganic solid film made of, e.g., WO.sub.3, MoO.sub.3 or the like. The second type of the ECDs utilizes an electrically-induced chemical reduction of a colorless liquid to produce a colored, insoluble film on the cathode surface.
In both of the above two types of the ECDs, the rate of coloration and erasure action considerably depends on the surrounding temperature since the coloration and erasure action is conduced according to electrochemical reactions. Especially, when constant voltage driving techniques are applied between display and counter electrodes of the ECD, the coloration and erasure action is variable according to the surrounding temperature. High temperatures accelerate the electrochemical reactions to thereby increase the color density.
In other words, non-uniformity in the coloration and erasure action inevitably occurred depending on the surrounding or atmospheric temperature inasmuch as a fixed voltage was applied to the electrodes for a constant time.
To make color density or shade constant, it might be possible to control the applied voltage pursuant to the surrounding temperature. However, high voltages may damage the electrochromic material. This technique of solving was therefore not practical.